Polyimides, process for producing the same and photosensitive composition containing the same

ABSTRACT

Polyimide is produced by reacting two kinds of diamine compounds consisting of diaminopolysiloxane and a hydroxyl group-containing diamine or three kinds of diamine compounds consisting of diaminopolysiloxane, a hydroxyl group-containing diamine and an aromatic or alicyclic diamine with a 4,4&#39;-(hexafluoroisopropylidene)diphthalic acid dianhydride, thereby once forming a polyamic acid, and subjecting the polyamic acid to polyimidization reaction. The resulting polyimide itself is soluble in low boiling organic solvents for general purpose use, typically methyl ethyl ketone. A photosensitive composition comprising the polyimide, a photo crosslinking agent and a photo acid-generating agent forms a negative type polyimide pattern upon development with an aqueous alkali solution.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to polyimides, a process for producing thesame and a photosensitive composition containing the same, and moreparticularly to polyimides capable of giving a negative type polyimidepattern upon development with an aqueous alkaline solution, a processfor producing the same and a photosensitive composition containing thesame.

2. Description of Related Art

So far used photosensitive resins are typically polyester acrylate,epoxy acrylate, etc. To obtain a desired pattern upon exposure of thesephotosensitive resins to light, an organic solvent is used as adeveloping agent. Such organic solvent developing type, photosensitiveresins have such a serious problem as an adverse effect on theenvironments in addition to safety or sanitary problem during workingdue to the use of the organic solvent.

In place of the organic solvent developing type, photosensitive resinshaving such problems, alkali-developable photosensitive resins based onnovolak resins, polyvinylphenol, etc. have been proposed and almost allof them have been utilized as positive type thin films having athickness of a several μm, but these positive type thin films have notalways satisfied the heat resistance, preservation stability, patternembedability, etc. required by FPC (flexible printed substrate)applications.

Furthermore, polyimide resins themselves are insoluble in an organicsolvent and therefore have so far relied on such a method of onceconverting them to organic solvent-soluble polyamic acids, followed bytheir polyimidization. However, some of polyimide resins themselves aresoluble in an organic solvent. For example, polyimide resins disclosedin JP-A-57-131227 and polyamide-imide resins disclosed in JP-A-59-145216are said to be soluble in an organic solvent and photosensitive.However, the organic solvent for that purpose is aprotic polar solventsincluding dimethyl-formamide, whereas acetone, benzene, cyclohexanol,etc., on the other hand, are used there for deposition of the resins.That is, the resins are insoluble in these latter organic solvents.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a polyimide by itselfsoluble in low boiling organic solvents for general purpose use,typically methyl ethyl ketone and capable of giving a negative typepattern upon development with an aqueous alkali solution, a process forproducing the same and a photosensitive composition containing the same.

According to the present invention, there is provided a novel polyimide,which is a copolymer comprising two kinds of diamine compoundsconsisting of diaminopolysiloxane and a hydroxyl group-containingdiamine or three kinds of diamine compounds consisting ofdiaminopolysiloxane, a hydroxyl group-containing diamine and an aromaticor alicyclic diamine, and a 4,4'-(hexafluoroisopropylidene)diphthalicacid dianhydride. Such a polyimide can be produced by reacting two kindsof diamine compounds consisting of diaminopolysiloxane and a hydroxylgroup-containing diamine or three kinds of diamine compounds consistingof diaminopolysiloxane, a hydroxyl group-containing diamine and anaromatic or alicyclic diamine with a4,4'-(hexafluoroisopropylidene)diphthalic acid dianhydride, thereby onceforming polyamic acid, and then polyimidizing the polyamic acid. Theresulting polyimide can be formed into a photosensitive composition byadding a photo crosslinking agent and a photo acid-generating agentthereto.

DETAILED DESCRIPTION OF THE INVENTION

For diaminopolysiloxane, one component of two or three kinds of diaminecompounds, which react with the carboxylic acid anhydride, compoundsrepresented by the following general formula can be used: ##STR1## whereR is a divalent hydrocarbon group having 2 to 6 carbon atoms, preferably3 to 5 carbon atoms; R₁ to R₄ are each a lower alkyl group having 1 to 5carbon atoms or a phenyl group; and n is an integer of 0 to 30,preferably 4 to 12.

The compounds include, for example, compounds whose R and R₁ to R₄ arethe following substituents in combination:

    ______________________________________                                        R          R.sub.1                                                                              R.sub.2     R.sub.3                                                                            R.sub.4                                    ______________________________________                                        (CH.sub.2).sub.3                                                                         CH.sub.3                                                                             CH.sub.3    CH.sub.3                                                                           CH.sub.3                                     (CH.sub.2).sub.4 CH.sub.3 CH.sub.3 CH.sub.3 CH.sub.3                          (CH.sub.2).sub.3 CH.sub.3 C.sub.6 H.sub.5 CH.sub.3 C.sub.6 H.sub.5                                              p-C.sub.6 H.sub.4 CH.sub.3 CH.sub.3                                          CH.sub.3 CH.sub.3                          ______________________________________                                    

Actually, the following commercially available products can be used:Toshiba Silicone products TSL9386, TSL9346 and TSL9306; TorayDow-Corning product BY16-853U, Shinetsu Chemical product X-22-161AS,Nippon Unicar product F2-053-01, etc.

The hydroxyl group-containing diamine for use in the present inventionincludes, for example, 4,4'-diamino-4"-hydroxytriphenylmethane,bis(4-amino-3-hydroxyphenyl)methane,4,4'-diamino-3,3'-dihydroxytriphenylmethane,4,4'-diamino-3,3',3"-trihydroxytriphenylmethane,2,2-bis(3-amino-4-hydroxyphenyl)propane,2,2-bis(3-amino-4-hydroxyphenyl)hexa-fluoropropane,4,4'-diamino-3,3'-dihydroxybiphenyl, etc. These hydroxylgroup-containing diamines, when the produced polyimide is to be used asa photosensitive resin, can be used so that the hydroxyl group contentis about 0.5 to about 3.0% by mole, preferably about 0.7 to about 2.5%by mole in the repetition units [(a) and (b) or (a) to (c) whichfollow]. Below about 0.5% by mole, the polyimide will be less soluble inan aqueous alkali solution, whereas above about 3.0% by mole it will betoo soluble therein.

The aromatic or alicyclic diamine for use in the present inventionincludes, for example, aromatic diamines such as3,3'-bis(aminophenyl)ether, 4,4'-bis(aminophenyl)ether,1,3-bis(4-aminophenoxy)benzene, bis[4-(4-aminophenoxy)phenyl]sulfone,bis[4-(3-aminophenoxy)phenyl]sulfone, 4,4'-diaminophenylsulfone,3,3'-diaminophenylsulfone, etc. or alicyclic diamines such as1,3-bis(aminomethyl)cyclohexane, 4,4'-bis(aminocyclohexyl)methane,3,3'-bis(aminocyclohexyl)methane, etc.

When two kinds of diamine compounds are used, diaminopolysiloxane isused in a proportion of about 20 to about 80% by mole, preferably about40 to about 70% by mole, whereas hydroxyl group-containing diamine isused in a proportion of about 20 to about 80% by mole, preferably about30 to 60% by mole, where total is 100% by mole. When less than about 20%by mole of diaminopolysiloxane is used, no film can be formed, whereasabove about 80% by mole development by an aqueous alkali solution cannotbe made any more. When less than about 20% by mole of hydroxylgroup-containing diamine is used, light-unexposed regions will beinsoluble in the aqueous alkali solution, whereas above about 80% bymole even light-exposed regions are soluble, but the difference indissolution rate between the light-exposed regions and thelight-unexposed regions will be smaller.

When three kinds of diamine compounds are used, diaminopolysiloxane isused in a proportion of about 20 to about 70% by mole, preferably about30% to about 50% by mole, hydroxyl group-containing diamine in aproportion of about 20 to about 70% by mole, preferably about 30 toabout 50% by mole, and aromatic or alicyclic diamine in a proportion ofabout 10 to about 60% by mole, preferably about 20 to about 40% by mole,where total is 100% by mole. When the aromatic or alicyclic diamine isused in such a proportion, the polyimide resulting there from will havea higher light transmission in the ultraviolet zone, for example, asatisfactory photosensitivity even to a film as thick as 50 μm. When thearomatic or alicyclic diamine is used in a proportion of more than about60% by mole, polyimide will have a reduced solubility in the lowerboiling organic solvents for general purpose use.

Reaction between a mixture of diamine compounds and a4,4'-(hexafluoroisopropylidene)diphthalic acid dianhydride representedby the following formula: ##STR2## is carried out preferably in anaprotic polar solvent such as dimethylformamide, dimethylacetamide,N-methyl-2-pyrrolidone, etc., but can be carried out even in a polarsolvent such as cresol, pyridine, etc. Actually, the carboxylic acidanhydride is dropwise added to a solution of the mixture of diaminocompounds in the polar solvent at about 0° to about 10° C. and subjectedto reaction at about 30° C. to 150° C., preferably at about 50° to about100° C., for about 2 to about 8 hours.

The resulting reaction product is polyamic acid as a polyimideprecursor, and thus is subjected to dehydration reaction forpolyimidization. Dehydration reaction is carried out, after adjustmentof the concentration to about 10 to about 20% by weight with a polarorganic solvent, if necessary, at a temperature of about 150° to about250° C., preferably about 180° to about 200° C., for about 2 to about 6hour, preferably about 2 to about 4 hour, preferably by using adehydrating agent such as acetic anhydride, pyridine, etc., where it isalso effective to use toluene, etc. to subject the formed water toazeotropic distillation.

Siloxanepolyimide, which is a polyimidazation reaction product, can bepresumed to be a block copolymer having repetition units (a) and (b)represented by the following general formulae, in case of using twokinds of diamine compounds, consisting of diaminopolysiloxane and4,4'-diamino-4"-hydroxytriphenylmethane as hydroxyl group-containingdiamine: ##STR3## Its weight-average molecular weights Mw (determined byGPC in terms of polystyrene) are about 10,000 to about 50,000,preferably about 15,000 to about 30,000.

Furthermore, in case of using three kinds of diamine compoundsconsisting of diaminopolysiloxane,4,4'-diamine-4"hydroxytriphenylmethane and 4,4'-bis(aminophenyl)ether,it can be presumed that a block copolymer having further repetitionunits (c) represented by the following general formula in addition tothe repetition units (a) and (b) represented by the foregoing generalformulae: ##STR4## Its weight-average molecular weights Mw are about10,000 to about 100,000, preferably about 20,000 to about 50,000, whichis higher than that in case of using the two kinds of diamine compounds.

The thus obtained copolymer is soluble in low boiling organic solventssuch as acetone, methyl ethyl ketone, methyl isobutyl ketone,tetrahydrofuran, ethyleneglycol monomethyl ether, chloroform, etc. oraprotic polar solvents such as dimethylformamide, dimethylacetamide,N-methyl-2-pyrrolidone, etc., and thus can be used as an organic solventsolution having a concentration of about 20-about 50 wt. % , preferablyabout 30-about 45 wt. %. The solution is admixed with a photocrosslinking agent and a photo acid-generating agent, and then dropwiseprovided onto an alkali-resistant substrate such as a quartz glasssubstrate, a copper substrate, etc. and subjected to spin coating (about500-about 2,500 rpm, preferably about 500-about 1,000 rpm, for about 10seconds) to form a film having a thickness of about 25 to about 50 μm,followed by prebaking at a temperature of about 70°-about 100° C.,preferably about 80°-about 90° C. for about 5-about 10 minutes, therebyremoving the solvent.

The thus obtained photosensitive polyimide-coated substrate is coveredwith a desired mask thereon and subjected to ultraviolet ray exposure ata dose of about 150-about 600 mJ/cm², preferably about 200-about 450mJ/cm² and then to postexposure baking at a temperature of about110°-about 140° C., preferably about 120-about 135° C. for about 5-about10 minutes, followed by development with an aqueous solution of analkaline compound such as potassium hydroxide, sodium carbonate,tetramethylammonium hydroxide, etc., at a temperature of about 30-about50° C., thereby giving a clear negative type pattern. The developingsolution herein used has a concentration of about 0.5-about 4% byweight, preferably about 0.5-about 3% by weight, and the developing timeis preferably within about one minute. After the development, waterwashing, drying and curing at about 160° C. for about 2 hours arecarried out.

Preferable photo crosslinking agent for use in the present inventionincludes, hydroxymethyl group-containing substituted phenols such as2-hydroxymethyl-4,6-dimethylphenol, 1,3,5-trihydroxymethylbenzene,3,5-dihydroxymethyl-4-methoxytoluene[2,6-bis(hydroxymethyl)-p-cresol],etc. The photo crosslinking agent can be used in a proportion of about 1to about 50 parts by weight, preferably about 3 to about 15 parts byweight, per 100 parts by weight of polyimide. Below about 1 parts byweight, the cross-linking density is so low that no satisfactory polymermatrix is formed and thus the film will be dissolved in the aqueousalkali solution, whereas above 50 parts by weight the solubility of thecomposition is lowered, so that a crystalline pattern will be formed onthe coated surface.

Photo acid-generating agent such asnitrobenzyl-9,10-diethoxyanthracene-2-sulfonate,diphenyliodonium-9,8-demethoxyanthracene sulfonate, etc. can be used ina proportion of about 1 to about 50 parts by weight, preferably about 3to about 20 parts by weight, per 100 parts by weight of polyimide. Belowabout 1 parts by weight, FPC pattern will be partially dissolved in theaqueous alkali solution and will be narrowed, whereas above about 50parts by weight a crystalline pattern will appear on the coated surfaceas in the case of the photo crosslinking agent.

The present invention provides a polyimide soluble in low boilingorganic solvent for general purpose use. A photosensitive compositioncontaining the present polyimide, a photo crosslinking agent and a photoacid-generating agent is developable in an aqueous alkali solution toform a negative type polyimide pattern with a distinguishedpatternability. When an aromatic or alicyclic diamine is simultaneouslyused as a diamine compound, a satisfactory photosensitivity even to athicker film can be given. Particularly in case of using an alicyclicamine, a satisfactory photosensitivity even to a film as thick as 70 μmcan be given.

PREFERRED EMBODIMENTS OF THE INVENTION

The present invention will be described in detail below, referring toExamples and Comparative Examples.

EXAMPLE 1

43.2 g (0.15 moles) of 4,4'-diamino-4"-hydroxytriphenylmethane and 132 g(0.15 moles) of diaminopolysiloxane (BY16-853U, product of Dow-CorningCo., USA; amine equivalent: 440) were charged into a separable flaskhaving a capacity of 1 L and 133.2 g (0.3 moles) of4,4"-(hexafluoroisopropylidene)diphthalic acid dianhydride as a solutionin 462 g of N-methyl-2-pyrrolidone was dropwise added thereto, keepingat a temperature of about 0-about 10° C. by ice cooling. After thedropwise addition, the solution was heated to 50° C. and stirred at thattemperature for 3 hours, and then heated to 200° C. and subjected todehydration reaction at that temperature for 3 hours. After thereaction, the reaction mixture was put into water and the product wasreprecipitated to obtain hydroxyl group-containing polyimide (hydroxylgroup content: 0.86% by mole).

100 parts by weight of the resulting hydroxyl group-containing polyimidewas admixed with 12.5 parts by weight of 2,6-bis(hydroxymethyl)-p-cresolas a photo crosslinking agent and 12.5 parts by weight ofdiphenyliodonium-9,10-methoxyanthracene-2-sulfonate as a photoacid-generating agent, and prepared into a solution having a solidconcentration of 40 wt. % in a solvent mixture of methyl ethyl ketoneand ethyleneglycol monomethyl ether in a ratio of 1:1 by volume.

The thus prepared photosensitive polyimide solution was spin coated ontothe lustrous surface of a copper foil at 600 rpm for 10 seconds,prebaked at 90° C. for 10 minutes to make once it into a film statehaving a thickness of 50 μm, covered with a mask (Photonix RP-1, productof Hitachi Chemical Co., Japan) thereon and exposed to ultraviolet raysat 300 mJ/cm². Then, after postexposure baking at 130° C. for 5 minutes,the mask-covered polyimide film was developed with an aqueous 2 wt. %tetramethylammonium hydroxide solution at 40° C. for 60 seconds, andthen washed with water at room temperature for one minute to obtain anegative type polyimide pattern.

Electron microscope observation of the resulting negative type polyimidepattern revealed that the pattern and line width were each 100 μm at100/100 (μm), showing a distinguished patternability without anyswelling.

EXAMPLE 2

In Example 1, the amount of 4,4'-diamino-4"-hydroxytriphenylmethane waschanged to 34.8 g (0.12 moles), that of diaminopolysiloxane to 158.4 g(0.18 moles), that of N-methyl-2-pyrrolidone to 489 g, and theconcentration of the aqueous solution of the developing agent to 2.5 wt.% , whereby a negative type polyimide pattern with a good patternabilitycould be likewise obtained. Hydroxyl group content of the hydroxylgroup-containing polyimide was 0.65% by mole.

EXAMPLE 3

In Example 1, 34.5 g (0.15 moles) of bis(4-amino-3-hydroxyphenyl)methanewas used in place of 4,4'-diamino-4"-hydroxytriphenylmethane, and thedose of ultraviolet ray exposure was changed to 450 mJ/cm² and theconcentration of the aqueous developing agent solution to 3 wt. %. Theresulting negative type polyimide pattern showed a good patternabilityas in Example 1. Hydroxyl group content of the hydroxyl group-containingpolyimide was 1.77% by mole.

The hydroxy group-containing polyimides obtained in the forgoingExamples 1 to 3 had weight-average molecular weights Mw of about 12,000to about 16,000.

COMPARATIVE EXAMPLE 1

In Example 1, when 96.6 g (0.3 moles) of benzophenonetetracarboxylicacid dianhydride was used as a tetracarboxylic acid dianhydride, theresulting polyimide (hydroxyl group content: 0.98 mol. %) showed nosubstantial light transmission in the ultraviolet region, particularlyat wave lengths of 350 to 450 nm.

COMPARATIVE EXAMPLE 2

In Example 1, when 93 g (0.3 moles) of oxydiphthalic acid dianhydridewas used as a tetracarboxylic acid dianhydride, the resulting polyimide(hydroxyl group content: 0.99 mol. %) had a light transmittance atultraviolet region of not more than 0.3, which was inferior to that ofExample 1. Solubility of the photosensitive composition in the solventmixture was only 20% by weight.

EXAMPLE 4

34.8 g (0.12 moles) of 4,4'-diamino-4"-hydroxytriphenylmethane, 18.0 g(0.09 moles) of 4,4'-bis(aminophenyl) ether and 79.2 g (0.09 moles) ofdiaminopolysiloxane (BY16-8531) were charged into a separable flaskhaving a capacity of 1L and 133.2 g (0.3 moles) of4,4'-(hexafluoroisopropylidene)diphthalic acid dianhydride was addedthereto as powders, keeping at a temperature of about 0°-about 10° C. byice cooling. Then, 400 g of N-methyl-2-pyrrolidone was added thereto todissolve the acid anhydride. After the dissolution, the solution washeated to 50° C. and stirred at that temperature for 3 hours, and thenheated to 200° C. and subjected to dehydration reaction at thattemperature for 3 hours. After the reaction, the reaction mixture wasput into water and the product was reprecipitated to obtain hydroxylgroup-containing polyimide (hydroxyl group content: 0.80% by mole).

100 parts by weight of the resulting hydroxyl group-containing polyimidewas admixed with 12.5 parts by weight of 2,6-bis(hydroxymethyl)-p-cresoland 12.5 parts by weight ofdiphenyliodonium-9,10-methoxyanthracene-2-sulfonate, and prepared into asolution having a solid content concentration of 40% by weight in asolvent mixture of methyl ethyl ketone and ethyleneglycol monomethylether in a ratio of 3:7 by volume.

The thus prepared plustosensitive polyimide solution was spin coatedonto the lustrous surface of a copper foil at 500 rpm for 10 seconds;prebaked at 90° C. for 10 minutes to make once it into a film statehaving a thickness of 50 μm, covered with a mask (Photonix PR-1) thereonand exposed to ultraviolet ray at 300 mJ/cm². Then, after postexposurebaking at 120° C. for 5 minutes, the mask-covered polyimide film wasdeveloped with an aqueous 2 wt. % tetramethylammonium hydroxide solutionat 40° C. for 60 seconds, and then washed with water at room temperaturefor one minute to obtain a negative type polyimide pattern.

Electron microscope observation of the resulting negative type polyimidepattern revealed that the pattern and line width were each 100 μm at100/100 (μm), showing a good patternability without any swelling.

EXAMPLE 5

In Example 4, 40.7 g (0.09 moles) of4,4'-[bis(3-aminophenoxy)phenyl]-sulfone was used in place of4,4'-bis(aminophenyl)ether. The resulting negative type polyimidepattern showed a good patternability as in Example 4. Hydroxyl groupcontent of the hydroxyl group-containing polyimide was 0.74% by mole.

EXAMPLE 6

In Example 4, 26.3 g (0.09 moles) of 1,3-bis(4-aminophenoxy)benzene wasused in place of 4,4'-bis(aminophenyl)ether. The resulting negative typepolyimide pattern had a good patternability as in Example 4. Hydroxylcontent of the hydroxyl group-containing polyimide was 0.77% by mole.

EXAMPLE 7

In Example 4, 12.8 g (0.09 moles) of 1,3-bis(aminomethyl)cyclohexane wasused in place of 4,4'-bis(aminophenyl) ether. The resulting negativetype polyimide pattern had a good patternability as in Example 4.Hydroxyl content of the hydroxyl group-containing polyimide was 0.93% bymole.

Hydroxyl group-containing polyimides obtained in the foregoing Examples4 to 7 had weight average molecular weights Mw of about 30,000 to about50,000.

What is claimed is:
 1. A polyimide, which comprises a copolymer of twokinds of diamine compounds consisting of diaminopolysiloxane and4,4'-diamino-4"-hydroxytriphenylmethane, and a4,4'-(hexafluoroisopropylidene) diphthalic acid dianhydride.
 2. Apolyimide according to claim 1, wherein the two diamine compoundsconsist of 20 to 80% by mole of the diaminopolysiloxane and 80 to 20% bymole of the 4,4'-diamino-4"-hydroxytriphenylmethane, total being 100% bymole.
 3. A polyimide according to claim 1, wherein in addition to twokinds of diamine compounds, an aromatic or alicyclic diamine is furtherused.
 4. A polyimide according to claim 3, wherein the three kinds ofdiamine compounds consist of 20 to 70% by mole of thediaminopolysiloxane, 20 to 70% by mole of the4,4'-diamino-4"-hydroxytriphenylmethane and 10 to 60% by mole of thearomatic or alicyclic diamine, total being 100% by mole.
 5. A processfor producing a polyimide, which comprises reacting two kinds of diaminecompounds consisting of diaminopolysiloxane and4,4'-diamino-4"-hydroxytriphenylmethane with a4,4'-(hexafluoroisopropylidene)diphthalic acid dianhydride, thereby oneforming a polyamic acid, and subjecting the polyamic acid topolyimidiazation reaction.
 6. A process according to claim 5, whereinthe two diamine compounds consist of 20 to 80% by mole of thediaminopolysiloxane and 80 to 20% by mole of the4,4'-diamino-4"-hydroxytriphenylmethane, total being 100% by mole.
 7. Aprocess according to claim 5, wherein in addition to two kinds ofdiamine compounds, an aromatic or alicyclic diamine is further subjectedto reaction.
 8. A process according to claim 7, wherein the three kindsof diamine compounds consist of 20 to 70% by mole of thediaminopolysiloxane, 20 to 70% by mole of the4,4'-diamino-4"-hydroxytriphenylmethane and 10 to 60% by mole of thearomatic or alicyclic diamine, total being 100% by mole.
 9. Aphotosensitive composition, which comprises a polyimide comprising acopolymer of two kinds of diamine compounds consisting ofdiaminopoly-siloxane and a hydroxyl group-containing diamine or threekinds of diamine compounds consisting of diaminopolysiloxane,4,4'-diamino-4"-hydroxytriphenylmethane and an aromatic or alicyclicdiamine and a 4,4'-(hexafluoroisopropylidene)diphthalic aciddianhydride, and a photo crosslinking agent and a photo acid-generatingagent.
 10. A photosensitive composition according to claim 9, whereinthe polyimide copolymer has a hydroxyl group content of 0.5 to 3% bymole.
 11. A negative polyimide pattern obtained by subjecting thephotosensitive composition according to claim 9 to light exposure,followed by development with an aqueous alkali solution.